1. Field of the Invention
The present invention relates to an organic electroluminescence device excellent in light extraction efficiency.
2. Description of the Related Art
Organic electroluminescence display devices (organic EL display devices) are self-luminescence type display devices and are for use in display and illumination. The organic EL display has such advantages of display performance that it is high in visibility, and free from viewing angle dependency, as compared to conventional CRTs and LCDs, and also has advantages in that display devices can be made lighter and thinner. Meanwhile, organic EL illumination has advantages, in addition to enabling lighter and thinner devices, in possibility of achieving lighting fixture having a shape that has not yet been achieved so far, by using a flexible substrate.
The organic electroluminescence display devices have superior features as described above, but the refractive index of each of layers constituting a display device, including a light emitting layer, is higher than the refractive index of air. For instance, in an organic electroluminescence display device, an organic thin-film layer, such as a light emitting layer, has a refractive index of 1.6 to 2.1. Therefore, emitting light is liable to be totally reflected at an interface, and the light extraction efficiency is less than 20%. Thus, the majority of light is lost.
As measures for improving the light extraction efficiency, there has been proposed a method in which a diffusion layer is provided adjacent to a transparent electrode on a light extraction surface side, and at least two different types of fine particles, which are different in average particle diameter by one digit or more, are dispersed in a resin in the diffusion layer (for example, see Japanese Patent Application Laid-Open (JP-A) No. 2005-190931), and the like.
However, the method described above in No. 2005-190931 has a shortcoming in that the light extraction efficiency is still insufficient.